nfp: bpf: pass raw data buffer to nfp_bpf_event_output()

In preparation for SKB-less perf event handling make
nfp_bpf_event_output() take buffer address and length,
not SKB as parameters.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Reviewed-by: Quentin Monnet <quentin.monnet@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>